4.6.4. *K*-Value Determination

The *K*-value was measured, according to the method described by Choi et al. [72] and by using high-performance liquid chromatography (HPLC) (1100 series; Agilent Technologies, Palo Alto, CA, USA). The nucleic acid-related compounds (NARCs) (adenosine triphosphate (*ATP*), adenosine diphosphate (*ADP*), adenosine monophosphate (*AMP*), inosine monophosphate (*IMP*), inosine, (*HXR*), and hypoxanthine (*HX*)) were analyzed under the following conditions: UV detection at 254 nm, the absorbed dose range (AUF) was 0.5, µBondapak column C18 (3.9 mm × 300 mm; water, Milford, MA, USA), and the column oven temperature was 40 ◦C, the flow rate was 2.0 mL/min, and the mobile phase was 1% triethylamine (pH 6.5) modified with 10% H3PO4. The K-value was calculated using the following equation:

$$K - value\ \left(\%\right) = \frac{\left[\left(HXR\right) + \left(HX\right)\right]}{\left[\left(ATP\right) + \left(ADP\right) + \left(AMP\right) + \left(IMP\right) + \left(HXR\right) + \left(HX\right)\right]} \times 100\tag{2}$$
